(a) Each induction system duct upstream
of the first stage of the engine supercharger and of the auxiliary power
unit compressor must have a drain to prevent the hazardous accumulation of
fuel and moisture in the ground attitude. No drain may discharge where it
might cause a fire hazard.

(2) Fire-resistant if it is in any fire
zone for which a fire-extinguishing system is required, except that ducts
for auxiliary power units must be fireproof within the auxiliary power
unit fire zone.

(c) Each duct connected to components
between which relative motion could exist must have means for flexibility.

(d) For turbine engine and auxiliary
power unit bleed air duct systems, no hazard may result if a duct failure
occurs at any point between the air duct source and the airplane unit
served by the air.

(e) Each auxiliary power unit induction
system duct must be fireproof for a sufficient distance upstream of the
auxiliary power unit compartment to prevent hot gas reverse flow from
burning through auxiliary power unit ducts and entering any other
compartment or area of the airplane in which a hazard would be created
resulting from the entry of hot gases. The materials used to form the
remainder of the induction system duct and plenum chamber of the auxiliary
power unit must be capable of resisting the maximum heat conditions likely
to occur.

(f) Each auxiliary power unit induction
system duct must be constructed of materials that will not absorb or trap
hazardous quantities of flammable fluids that could be ignited in the
event of a surge or reverse flow condition.